Metal working machines are well known. A conventional metal working machine typically includes a power drive unit, such as an electric, hydraulic, or pneumatic motor; a suitable cutting tool, such as a drill, boring tool, probe or the like; and a tool holder for connecting the cutting tool to the power drive unit. The tool holder typically includes a socket or sleeve member, which is mounted directly to the power drive unit, and which is adapted to support the cutting tool in order to connect the cutting tool to the power drive unit.
A typical cutting tool has a cylindrical shank with a specific diameter that fits within a close tolerance in the sleeve member of the tool holder. The shank may be provided with a single flat, or multiple, usually two, axial aligned flats, which are typically machined along the peripheral surface of the shank. This type of shank is commonly referred to as a “Weldon Shank”. The sleeve member supports a setscrew for each flat. The setscrews are adapted to be tightened against the flats. The force of each setscrew is transmitted to the shank, causing a portion of the shank, opposite (i.e., 180 degrees from) the flats, to meet or engage an inner surface of the sleeve member to secure the cutting tool therein.
The aforementioned tool and holder arrangement theoretically results in two points, or a single line, of contact between the cutting tool and the tool holder that is parallel to the toolholder. These two points of contact allow a cutting tool to move or vibrate relative to the tool holder, creating chatter under certain conditions. This is due to the combined natural frequencies of the power drive unit, the cutting tool, and the tool holder and the harmonic nature of these elements when operating the cutting machine at various parameters. When the chatter occurs, minute particles of material are removed from either the shank or the sleeve member. These particles typically become embedded in one of the opposing mating surfaces of the shank or the sleeve member, normally in the shank because it is softer than the sleeve member, also commonly known as fretting.
The aforementioned tool and holder arrangement has another drawback. When tightening the setscrews against the flats, the center of the shank or cutting tool is often offset from the center of the sleeve member or tool holder.
What is needed is a tool and holder arrangement, which eliminates or minimizes vibration that results in chatter, and which results in less offset between the center of the cutting tool and the center of the tool holder.